Rectifying column



April 20, 1943. H, s, LEcKY REGTIFYING COLUMN Filed July 6, 1940JNVENTOR. h5.' Eck v;

'Patented Apr. 20,- 1943 nEc'rIFYrNG COLUMN Herbert s. becky, WestLafayette, ma., assignmto Purdue Research Foundation, West Lafayette,Ind., a corporation of Indiana Application July 6, 1940, Serial No.344,254

3 Claims.

It is the object of my invention to produce a rectifying column ofimproved performance characteristics. More specifically, that object'lsto produce a rectifying column which will give close rectificationwithout requiring excessive height of column; which maintains itseffectiveness with increasing reflux rate until well toward the oodingpoint, as measured in the number of equivalent theoretical plates perfoot; which has a high through-put; which has a very small H. E. T. P.(height equivalent to a theoretical plate); and which is relativelyinexpensiveto make.

In carrying out my invention, I provide in the column a helicalpermeable packing. This helical permeable packing may be of Variousforms. Among those forms are a helix of wire screen, deslrably a negauze; a helix formed by a wrapping of a close-wound helical wirespring; and a helix of textile fabric, suitably supported in the helicalform, as for instance a hollow tubular fabric held tubular by aninserted helical spring and wound in helical form to produce the helicalpermeable packing.

This helical permeable packing has several advantages. It provides acontinuous helical passage for the upwardly moving vapor. At the sametime it provides the same continuous helical passage for the downwardlymoving reflux. It permits that reflux to permeate the meshes of thepermeable packing, and so to form a fllm which on both its sides isexposed to the vapor. In consequence, there is evaporation from andcondensation upon the surface of the reflux on both the upper and lowersides of the helical permeable packing.

The accompanying drawing illustrates my invention: Fig. 1 is a sectionaldiagrammatic view, partly broken away, showing a rectifying columnembodying my invention in a simple form; Fig. 2 is a plan view of ascreen-washer which I may use for building up a screen helix; Fig. 3 isa side elevation of thescreen-washer of Fig. 2, sprung apart intohelical form, and showing in dotted lines fragments of associatedsimilarly sprung-apart screen-washers to indicate the,

manner of assembly to make the complete screen helix; Fig. 4 is a planview of a screen-washer similar to Fig. 2, but with an edge binding ofmetallic foil to reduce leakage around the edge; Fig. 5 is an enlargedfragmentary section, in partial elevation, of a multiple column,consisting of several coaxial annular columns of different diameters,with each column provided with its own helical-screen packing; Fig. 6 isan enlarged fragmentary dead-section on the line 6-6 of Fig. 5, with thescreen helix provided with inner and outer bindings of metallic foil;Fig, 7 is a transverse section of a modified form of column in processof manufacture, showing a central tube with a projecting helical row ofpins on lwhich a permeable packing is being woven out of Wire; Fig. 8 isa fragmentary front elevation of the central tube of Fig. 7, with itshelical row of pins; Fig. 9 is a view similar to Fig. 7, but with thehelical permeable packing consisting of a ribbon of textile or gauzeinterlaced on the helical row of pins; Fig. 10 is a fragmentary verticalsection through a column in which the packing is a helical tube offabric, such as a tubular Shoestring, having within the fabric tube ahelical spring which is wound with the Shoestring into the larger helixof the packing; Fig. 11 is a fragmentary vertical dead-section of amodified form of screen-washer similar to that of Figs. 2, 3, and 4 butwith the inner and outer angularly bent edge portions to reduce edgeleakage in the co1- umn; and Fig. 12 is a transverse section through acolumn having a bundle of rectifying tubes.

The main structural features of the rectifylng column, apart from thepacking, may be of any usual or desired construction. One effectivedesign of column is shown in Fig. 1. At the bottom there is astill-chamber I5, which contains the liquid I6 to be rectified, andwhich may be heated in any suitable way, for instance by a burner I1 asshown. The lower end of the column 2| is conveniently set directly inthe mouth of the still-chamber I5. A vapor chamber 22 is located abovethe column 2|; and if it is separatable from the column, as it may be,the vapor-inlet tube 23 with which it is provided at the bottom has aclose-fitting joint 24 with the upper end of the column. A thermometerwell 25 is usually provided at the top of the vapor chamber 22, forreceiving a thermometer 26. The vapor chamber 22, as shown, has anoblique downward outlet tube 21, provided with a stopcock 28; and theentrance to that tube 21 lies below the lower end of an obliquecondenser 29, the upper end of which may be connected by a dischargetube lto a drip vent 3| to which the outlet tube 21 also leads. Thecondenser 29 has a suitable cooling jacket 32, in the usual manner ofcondensers: and the rectifying column 2| may have a vacuum jacket 33,surrounded if desired by an electrical heating coil 34. As so fardescribed, the structure is more or less conventional, and may be variedalong any conventional or desired lines.

The rectifying column may have a single rectifying tube 40, as is shownin Fig. 1; or may have a. plurality of rectifying tubes, for exampleeither arranged in a bundle of tubes 40 as is shown in Fig. 12 or as agroup of coaxial tubes 4I, 42, and 43'as is illustrated in Fig. 5. Thetube 40,'or each tube 40, or the central tube 4I, is provided with anaxialfrod (or closed-end tube) 44.

Within the tube 40, or each tube 40, or within each of the tubesv 4l,42, and 43, I place my new helical permeable packing 50. This packing islocated between the inner surface of the tube within which it lies andthe outer surface of the next adjacent cylinder within such tube,whether that next adjacent surface be of the axial rod (or closed-endtube) 44 or one of the inner tubes 42 or 4|.. According to my presentpreferences, the helical permeable packing is most conveniently made ofwire screen, desirably a fine gauze, made of wires or films of amaterial which is not attacked, or at most not too rapidly attacked, by

the fluids which come in contact with it in the rectifying process.

' A simple Way of making the helix of screen is to' make rst a series ofscreen-washers 5i, as is shown in Fig. 2, havinga suitable outerdiameter to fit closely within the tube whichis to receive it (the tube40, 4l, 42, or 43) and a` suitable inner diameter to t closely upon thecylinder member which it surrounds (the tube '42, the tube 4l, or thecentral rod 44) The screen-washer 5l is cut along a radial line 52, tomake a split-washer;

and the split-washer is spread out into the form of a single-turn helixas is illustrated in Fig. 3. The helical packing is produced by puttingtogether a series of these single-turn helixes, end to end, and suitablyfastening together the adjacent ends of the several single-turn helixes,as by.

overlapping such adjacent ends and spot-Welding them together. In thisway, al multipleL-turn helix of any desired length and number of turns'may be built up. The number of turns may be as many as several hundred,and the length may be many feet; the number of theoretical platesincreases in substantial proportion to the length. If desired, two ormore helixes may be interthreaded together, as is done for the screenhelixes immediately within the tubes 42 and 43 in Fig. 5, to make amultiple helix in which each individual helix has a thread-pitch whichis a multiple of the distance between the adjacent :screen layers.

The helix 50, whether it be a single helix as is shown in the tube 40 ofFig. 1 and the tub '.-s 4l of Fig. 5, or a multiple helix as shownwithin the tubes 42 and 43 of Fig. 5, is thenmounted in place Within thetube which is to-receive it (the tube 40, 4I, 42, or 43) and around thenext inward cylindrical surface (the rod 44, or the tube 4| or 42 as thecase may be). The helical .screen should have a tight joint with bothcylindrical surfaces which it abuts-the inner surface of the tubesurrounding it and the outer surface of the cylinder which it surrounds.This is in order to prevent leakage past the edges of the helicalscreen. This tight joint, which need not be absolutely tight although itis desirable to have it ias tight as possible, may be obtained in manyways. In one way, the glass tubes associated with any helix may beheated to the softening point, to produce a owing of the glass aroundthe helix edges. Instead of or in addition, the washers 5l may beprovided with a binding 53 of metal foil, crimped in place on thewashers.` This metal-foil binding may, if desired be provided on onlythe outer edge of the screen-washer, as is illustrated in Fig. 4, or onboth edges as is illustrated in Fig. 6. The metal-foil binding hugs theadjacent glass wall and materially reduces leakage. Alternatively, thewasher 5I may be cupped, if desired only at its edges. as is shown in`Fig. 11, -to provide oblique flanges 54 which press ,provided witha'nuniberV of outwardly projecting radial pins 60, arranged on that rodor tube 44 in a helix as is clear from Fig. 8. The helical permeablepacking is built on these helically arranged pins 60, as by circularlyinterweaving wires or threads 6l on such pins, as is shown in Fig. 7.Instead of the wires or threads 6| of Fig. 7, I may interweave on thepins 60 a at ribbon 62 of woven or matted material, such as cotton.

The helix thus formed on the central rod or tube 44 has the surroundingtube placed over it. with a tight nt; and in case the helix is built upof wires or other non-inflammable material the tightness of the fit maybe augmented by heating that surrounding tube sufficiently to soften theglass and let it contract on the helix.

Another variation is shown inFig. 10. Herea tubular fabric member 65,such as a tubular shoestring in small columns, is wound helically on thelcentral rod or tube 44, and surrounded by the next alone, without thecovering of fabric 65; although I prefer that that covering of fabric 65be used.

In operation, the liquid to be rectified is placed in the still-chamberI5, and suitably heated to produce evaporation of its contents. ,Thevapors rise through the column 2|, which may be heated; travel in thehelical path or paths provided by the helical permeable packing orpackings; and condense in the condenser 29.' There may be one helicalpath, as in Fig. l, or several parallel helical paths, as in Figs. 5 and12. The condensate or reflux tends to run backward along-the samegeneral helical path or paths in which the vapors are ascending, and wetand permeate the helical permeable packing or packings. Thus the refluxand the vapors are in contact, and there .is a constant linterchange ofmaterial between the vapor state and the liquid state as is common inrectifying columns. But with my helical permeable packing, thisinterchanging of phase between the vapor state and the liquid stateoccurs on both surfaces of the helical permeable packing, the upper andlower surfaces in Fig. 5 for instance, and the liquid not only flowsdown the helical path but to some extent permeates the and descendingliquid (reiiux) In other words. because the liquid wets the wire screenor other helical permeable packing, and exposes a liquid surface at bothsides of such packing, there are two surfaces of liquid-phase contact,in a long path for both the liquid and the vapor to travel for arelatively short length of the complete column.

The vapor which finally passes out at the top of the column 2| passesinto the vapor chamber 22, and is condensed in the condenser 29, anddrawn off by way of the drip vent 3l, by which the take-oil? and hencethe ratio of takeoff to reflux are controlled. Very close cuts may beobtained. The boiling points of the several cuts are determined by thethermometer 2E.

My improved column has the unexpected property that its eiectiveness asmeasured in H. E. T. P, is maintained with increasing reflux rate untilclose to the flooding point. This is a desirable and distinguishingfeature; because l most types of rectifying columns are more efilcientat lower vapor velocities, so that for their emciency it is necessary tokeep the reflux rate or through-put relatively low.

Combined with` this maintenance of eiectiveness at high reflux rate, myimproved column also has a very small hold-up-that is, it has a verysmall quantity of liquid in the column in operation, so that sharpseparation between cuts is obtainable.

Further, there is a very low pressure-drop in my column, for thepressure at the bottom ls very little higher than at the top.

My column has the further desirable feature that it can be constructedto have increased height eiilciency at the expense of through-put orincreased through-put at the expense of height eiliciency by placing theturns of the helixes closer together or farther apart, as may bedesired.

I claim as my invention:

l. In a rectifylng column having means for connecting the lower part toa still-chamber and the upper part to a condenser, a helical permeablemember for supporting a lm of reflux liquid which by reason of thepermeability of said helical permeable member is exposed over both itsupper and lower sides to vapor ascending in a helical path provided bysaid helical permeable member, and means for closing the inner and outersides of said helical path'.

2. In a rectifying column having an impermeable tubular shell of whichthe lower part is provided with means for admitting vapor and foremitting liquid and the upper part is provided with means for emittingvapor and admitting reflux liquid, a helical permeable packing fittingwithin said shell and contiguous with the inner surface of said shell,and means for closing theinner side of that helical path, said helicalpermeable packing consisting of a helix of wire screen and engaging saidshell and said closing means in a manner which substantially preventsshort-circuiting ilow of liquid between adjacent turns of said helicalpath.

3. In a rectifying column having an impermeable tubular shell of whichthe lower part is provided with means for admitting vapor and foremitting liquid and the upper part is provided With means for emittingvapor and admitting reflux liquid, a helical permeable packing fittingwithin said shell and contiguous with the inner surface of said shell,and means for fusing the inner side of that helical path, said .,llcalpermeable packing consisting of a helix of textile fabric and engagingsaid shell and said closing means in a manner which substantiallyprevents short-circuiting flow of liquid between adjacent turns of saidhelical path.

HERBERT S. LECKY.

Patent No. 2,517,101.

cERfrIFIcATx oF connEcTIoN.

- April 2o, 191,5.

HERBERTS. LECKY.

It is hereby certified that error appears. in the printed specificationofthe above numbered patent requiring correction as follows: Page 2,second column, line 58, for 'with' read wthin'; and that the saidLetters Patmt should. be read wim 'this correction therein that the samemay conform to the record of the case inthe. Patent Office.

signed ma sealed this 1st day of June, A. D. 19M.

Henry Van Arsdale, (Seal) Acting Conmiasioner of Patents.

